Recently, organic light-emitting elements (organic light-emitting devices, OLED in short) have attracted attention due to their properties such as high luminance, high refresh rate, wide color gamut, etc., since these properties allow the OLED to be more suitable for application in portable electronic devices.
In general, an organic light-emitting element comprises an anode, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode sequentially deposited by vacuum deposition or coating methods. When a voltage is applied on the organic light-emitting element, holes and electrons are implanted by the anode and the cathode respectively into the organic layer(s). The implanted holes enter the light-emitting layer through the hole transport layer, and the electrons migrate into the light-emitting layer through the electron transport layer. In the light-emitting layer, electrons combine with holes to generate excitons. The excitons relax via a light-emitting mechanism to emit light.
The reason for manufacturing an organic light-emitting element using a multilayer thin film structure encompasses the stability of the interfaces between the electrodes and organic layers. Additionally, there is a significant difference between the migration rates of electrons and holes in an organic material. Accordingly, if a hole transport layer and an electron transport layer are suitably selected, the holes and electrons can be transported into the light-emitting layer efficiently to improve the luminescent efficiency of the element.
However, in actual manufacturing process of a display, it is difficult to obtain an organic material meeting all aforementioned requirements. For example, it is problematic in maintaining the property of an organic light-emitting element in emitting blue light while still prolong the life of the element. Therefore, it is urgent to develop an organic light-emitting element with longer life and high performance.